This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application 2001-065569 filed on Mar. 8, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to a vehicle brake apparatus. More particularly, this invention pertains to a hydraulic brake apparatus suitable for an electric vehicle to perform regenerative braking.
A known hydraulic brake apparatus for a vehicle is disclosed in U.S. Pat. No. 4,126,996 published on Nov. 28, 1978. This brake apparatus includes a hydraulic pressure generator for generating a power pressure irrespective of operation of a brake pedal and outputting the power pressure. A regulation valve regulates the power pressure outputted from the hydraulic pressure generator to a pressure corresponding to the operation force applied to the brake pedal and outputs the pressure. A master cylinder is provided with a master cylinder pressure chamber and an auxiliary pressure chamber connected to the output side of the regulation valve. The master cylinder is operated by an auxiliary pressure in the auxiliary pressure chamber to generate a master cylinder pressure corresponding to the auxiliary pressure in the master cylinder pressure chamber. A wheel brake cylinder is operated by the master cylinder pressure to apply a braking force to a wheel. In this hydraulic brake apparatus, the operation (depression) force of the brake pedal which is necessary for applying a certain braking force to the wheel is relatively small.
In the case of an electric vehicle performing regenerative braking, the braking force by regenerative braking takes precedence over the braking force by the hydraulic pressure in the wheel cylinder. Further, the braking force associated with regenerative braking varies by factors such as the charging condition of the battery and the vehicle speed. Thus, it is necessary to modulate the hydraulic pressure in the wheel cylinder to be less than the pressure corresponding to the operation force of the brake pedal or the braking force required by a driver through a relatively simple and not excessively expensive construction.
However, in the known hydraulic brake apparatus, because the auxiliary pressure chamber communicates with the output side of the regulation valve, the auxiliary pressure in the auxiliary pressure chamber is equal to the pressure outputted from the regulation valve corresponding to the operation force of the brake pedal. For that reason, the master cylinder pressure corresponding to the operation force of the brake pedal is supplied to the wheel cylinder. Thus, if the known apparatus is applied to an electric vehicle which performs regenerative braking, a braking force greater than that required by the driver is applied to the wheel by the regenerative braking force.
A need thus exists for a vehicle hydraulic brake apparatus which is not as susceptible to the drawbacks mentioned above.
According to one aspect, a hydraulic brake apparatus for a vehicle includes a hydraulic pressure generator which generates a power pressure irrespective of brake pedal operation and outputs the power pressure, a regulation valve which regulates the power pressure outputted from the hydraulic pressure generator to a predetermined pressure corresponding to the brake pedal operation force and outputs the predetermined pressure, and a master cylinder having an auxiliary pressure chamber which is connectable to an output side of the regulation valve and a master cylinder pressure chamber. The master cylinder is operated by an auxiliary pressure in the auxiliary pressure chamber to generate a master cylinder pressure corresponding to the auxiliary pressure in the auxiliary pressure chamber. A wheel brake cylinder is operated by the master cylinder pressure to apply a braking force to a wheel. Further, a pressure modulation device is disposed in a pressure passage connecting the output side of the regulation valve to the auxiliary pressure chamber to modulate the auxiliary pressure to a pressure less than the predetermined pressure outputted from the regulation valve.
According to another aspect, a hydraulic brake apparatus for a vehicle includes a hydraulic pressure generator which generates a power pressure irrespective of operation of a brake pedal and outputs the power pressure, a regulation valve which regulates the power pressure outputted from the hydraulic pressure generator to a predetermined pressure corresponding to an operation force of the brake pedal and outputs the predetermined pressure, and a master cylinder having a first master cylinder pressure chamber and an auxiliary pressure chamber which is connectable to an output side of the regulation valve. The master cylinder is operated by an auxiliary pressure in the auxiliary pressure chamber to generate a master cylinder pressure corresponding to the auxiliary pressure in the auxiliary pressure chamber. A first wheel brake cylinder is operated by the master cylinder pressure to apply braking force to a wheel of the vehicle. A pressure modulating means modulates the auxiliary pressure to a pressure less than the predetermined pressure outputted from the regulation valve.
According to a further aspect, a hydraulic brake apparatus for a vehicle includes a pump for generating a power pressure irrespective of operation of a brake pedal, a regulation valve connected to the pump to regulate the power pressure outputted from the pump to a predetermined pressure corresponding to an operation force of the brake pedal, and a master cylinder having an auxiliary pressure chamber which is connectable to an output side of the regulation valve and a first master cylinder pressure chamber, with the master cylinder being operated by an auxiliary pressure in the auxiliary pressure chamber to generate a master cylinder pressure corresponding to the auxiliary pressure in the auxiliary pressure chamber. A first wheel brake cylinder receives the master cylinder pressure to apply a braking force to a wheel of the vehicle. A first valve is located in a pressure passage connecting the regulation valve to the auxiliary pressure chamber, and a second valve is located in a pressure passage connecting the auxiliary pressure chamber to a reservoir. In addition, a control device controls the first and second valves to modulate the auxiliary pressure to a pressure less than the predetermined pressure outputted from the regulation valve.